Recently, Kim and Deal discovered a new soluble hemoprotein from pig liver. It was tentatively named hemoprotein H-450 and purified to homogeneity. Though its function was not determined, H-450 is probably a soluble b-type cytochrome from mammalian liver (Biochemistry (1976) 15, 4925). The immediate objectives of this proposal are (1) to develop a new, improved purification procedure of H-450 from pig and rat tissues by using immunoassay methods, (2) characterization of the native H-450 and its apoprotein, and (3) the discovery of its biological function. The long term objectives are (1) to search for the physiological role of H-450 in mammalian tissues; (2) to elucidate its primary and tertiary structure; (3) to study its physiochemical properties and the interaction between proheme and apoprotein; (4) to investigate its relationship to various conditions of liver diseases, inborn-error metabolism, aerobic glycolytic metabolism in tumor tissues, and oxidative metabolism; and (5) to search for a possible new electron transport system in which H-450 could be involved.